The present invention relates generally to the field of sensing devices, their use and methods for their manufacture, and more particularly, to a radiation sensing planar monolithic silicon integrated circuit for determining the azimuth and elevation of incident radiation. The device and method is particularly well suited for integration in a single planar monolithic silicon IC (Integrated Circuit) chip along with additional circuitry for use in navigation, guidance and control systems, for example systems in space or used for space exploration, or other systems including positional control of systems relative to incoming radiation. The present invention relates to a particular class of radiation sensing devices called sun pointers and is useful as part of a miniaturized system for space navigation for satellites, particularly very small satellites, or other exploratory space vehicles, including robotics, where size, low power, low signal level (optical and electronic) sensitivity, angular sensitivity (ability to detect very small changes in azimuth and elevation of incident radiation), large dynamic range and an ability to minimize the number of constituent parts is important.
Light (radiation) inherently contains direction and amplitude characteristics. Consequently, light (radiation), when properly detected and analyzed, is useful in navigational and positional control applications. Sensors that function in response to incident radiation are known in the art. One example of a guidance or positioning system that uses a light or radiation source such as the sun for positioning is known in the art as a sun pointer. Sun pointers provide the azimuth and elevation of the sun relative to a space platform's location and thus provide necessary information for navigation in space. Monolithic silicon integrated circuit chips manufactured with state of the art planar technology are known to provide the greatest degree of miniaturization of electronic functions while at the same time providing large sensitivity to detecting small electronic signals and simultaneously providing large dynamic range. A sun (radiation) pointing device is disclosed which combines sun pointing capability within a single planar monolithic silicon IC chip, without mechanical apertures or pin holes for directing incident radiation, with large dynamic range, with state of the art angular, electrical and optical sensitivity and which can be reduced in size (miniaturized) or scaled to nanometer dimensions the same as state of the art monolithic silicon IC technology
U.S. Pat. No. 4,611,914, entitled Sunbeam Incident Angle Detecting Device, illustrates a sun pointer system for determining position relative to a light source. The technology disclosed in the '914 patent uses a pair of solar cells disposed at a known angle, other than zero, to each other. When radiation impinges, the current produced by the radiation in the solar cells is used to determine the incident angle of the radiation. This angle is then used to determine the relative position of a satellite to a light source.
Efforts to reduce the size of sun pointing devices or systems such as disclosed in the '914 patent have utilized various technologies including microelectonics. In all cases the reduction efforts have resulted in structures in which the radiation detecting elements are fabricated essentially in a single plane. Even in cases where there is more than a single radiation detecting element and even when these various radiation detecting elements are placed at different angles relative to each other and including orthogonal placement, the radiation detecting elements are still essentially located in a single plane. This has resulted in devices with mechanical slits, pinholes or alignment apertures to direct impinging radiation (sun light) using mechanical alignment and to prevent the impinging radiation from striking the entire photo detecting element surface. Azimuth and elevation information on the incident radiation is only available in such mechanical alignment systems or devices if the radiation is positionally directed, by an aperture, slit or pinhole system, onto the detecting elements in a particular manner.
One such existing sun pointer system employs electro-optical sensing devices in conjunction with mechanical alignment to guide the impinging light or radiation relative to the electro-optical sensors. FIG. 1 of the present invention illustrates a sun pointer system that employs such a prior art design. The sensing element of the system is a photodiode array. Light (radiation) impinges the array through a mechanical entrance slit providing direction and amplitude information to the system via photocell output signals, amplifiers, and buffer storage.
Pointing systems of this type require that the impinging radiation (light) pass through a mechanical aperture to control where the radiation strikes the photo diode array or detector surfaces. Such a mechanical opening is an integral part of such sensors and azimuth and elevation information cannot be obtained without them. As such, the mechanical pinhole, aperture or slit serves as a major limitation of such systems. This makes the systems, even those which are miniaturized to some extent, incompatible with being integrated into a single monolithic silicon integrated circuit chip using modern planar technology, makes the systems physically larger than otherwise required since the mechanical apertures must reside a fixed physical distance from the photo detector/sensor surface or the plane of the photo detector/sensor surfaces, reduces (sets a limit to) the sensitivity of the basic device to very small changes in directional information in the incident radiation and limits the ability to scale or shrink the device to smaller dimensions to be compatible with and integrated in a nanoscale monolithic silicon IC chip.
U.S. Pat. No. 5,517,017 (the '017 patent or Yamada) uses a form of mechanical aperture. In one embodiment, they use a pinhole (see FIGS. 2 and 4) and in another embodiment different shaped apertures, but all are essentially mechanical apertures to direct light onto a set of surface photo detectors essentially in one surface plane. In addition, the detectors in this patent are photo diodes which have no amplification and thus will not be capable of detecting small radiation signals to the same level or degree as devices with integral amplification. Further, the '017 patent relates to a device made with thin film hybrid technology and cannot be reduced in size or scale to the same degree as a monolithic silicon IC chip and cannot be integrated into a single monolithic silicon IC chip.
The existing technology for determining azimuth and elevation of incident radiation which relies on radiation traveling through a pinhole, aperture or slit has disadvantages. Present designs are not compatible with existing planar monolithic silicon integrated circuit technology, thus single planar monolithic IC chip solutions for positioning or navigation using the mechanical aperture technology are not available. The need for a mechanical pinhole or aperture makes this solution physically larger and difficult to form single chip guidance systems and in addition, the requirement for a mechanical slit or aperture makes the embodiment less sensitive to angular changes in incident radiation than it would have to be without the mechanical slit since the mechanical apertures are required to be some fixed physical distance from the detector or sensor surface in order to work. As the requirement for miniaturization increases, the physical size and sensitivity limitations become important and the system cannot be physically reduced enough in size.
What is needed, but currently unavailable in the art, is an improved sun pointing device that is inherently small in size, capable of accurately providing information relating to azimuth and elevation of incident radiation, light weight, has minimal power requirements for its use, capable of being integrated as a monolithic IC in silicon, capable of being scaled to very small dimensions (nanometers) and which does not have the requirement for impinging radiation to pass through a mechanical slit, pin hole or aperture in order to provide azimuth and elevation information. In addition a device is needed which is completely compatible with monolithic integrated circuits technology and which can be integrated into a single piece of silicon to form a single monolithic silicon integrated circuit comprising a guidance system.
It is to the provision of a device capable of providing azimuth and elevation information relative to incident radiation to the surface of a monolithic silicon IC chip, without the use of a mechanical slit or aperture to guide the radiation, that includes integral signal amplification and is capable of being integrated with a single monolithic silicon IC chip with other circuitry that the present invention is primarily directed. The present invention works with radiation incident on the entire detector/sensor surface.